Cathode/membrane assemblies of the aforedescribed type are utilized to provide the cathode which may be required in SPE water electrolysis. The expression "SPE" refers here to solid polymer electrolyte processes.
Such processes include electrolysis for the generation of hydrogen using an electrolyte forming an acidic medium, and SPE hydrochloric acid electrolysis and even electrolysis of sulfuric acid may be carried out in these processes. Other processes in which such units are applicable are the cathodic generation of hydrogen concurrently with anodic oxidation of sulfur dioxide in sulfuric acid electrolyte. A specific example of this latter process is the electrochemical oxidation of SO.sub.2 from exhaust gases concurrently with the generation of H.sub.2 and the analogous electrolysis in the sulfuric acid hybrid process.
Cathode/membrane assemblies of the aforedescribed type can make use of the commercial membrane material known under the name of NAFION.RTM. which has been coated on both sides with platinum, the latter serving as a catalyst (e.g. for use in the sulfuric acid hybrid circulation process). The assembly thus constituted has been found to be applicable in an SPE electrolysis cell, i.e. an electrolysis cell using an ion exchange membrane as the separator.
The anolyte can be SO.sub.2 -saturated sulfuric acid. An additional liquid catholyte is not required.
In the operation of such electrolysis cells it has been found that there is a tendency to cathodically reduce some of the SO.sub.2 and thus produce sulfur or hydrogen sulfide which can act as poison to the catalytically active platinum coating on the cathode side. This, of course, defeats the purpose of the cathode coating and efforts to eliminate the problem have been frustrated by the fact that up to now no proton-conductive ion exchange material has been found which is not also at least somewhat permeable to sulfur dioxide.